Mesothelioma

About mesothelioma

Mesothelioma is a cancer that starts in cells in the linings of certain parts of the body, most commonly the linings of the chest or abdomen (belly).

Cancer starts when cells start to grow out of control. Cells in nearly any part of the body can become cancer. See What Is Cancer? to learn more about how cancers start and spread.

The mesothelium

Special cells called mesothelial cells line the inside of the chest, abdomen, and the space around the heart. These cells also cover the outer surface of most of your internal organs. The lining formed by these cells is called the mesothelium.

The mesothelium helps protect your organs by making a special lubricating fluid. This fluid allows organs to easily slide against each other, such as when your lungs expand and contract inside your chest when you breathe. The mesothelium has different names in different parts of the body:

• The pleura covers the lungs and the space in the chest that contains the lungs.
• The peritoneum lines the inside of the abdomen and covers many of the organs in the abdomen.
• The pericardium covers the heart and the space that holds the heart in the chest.
• The tunica vaginalis lines the testicles.

A cancer that starts in any of these places is called mesothelioma. In the past, it was often known as malignant mesothelioma.

Types of mesothelioma

Mesotheliomas can start in 4 main parts of the body.

• Pleural mesothelioma (formerly known as malignant pleural mesothelioma, or MPM) starts in the chest. It is by far the most common type, making up more than 8 out of 10 mesotheliomas.
• Peritoneal mesothelioma starts in the abdomen. It accounts for most of the remaining mesotheliomas.
• Pericardial mesothelioma starts in the covering around the heart and is rare.
• Mesothelioma of the tunica vaginalis is a very rare tumor that starts in the covering layer of the testicles.

Mesotheliomas are grouped into 3 main subtypes based on how the cancer cells look (their histology):

• About 6 out of 10 mesotheliomas are epithelioid. This subtype tends to have a better outlook (prognosis) than the other types.
• About 1 out of 10 mesotheliomas are sarcomatoid. These include a subtype known as desmoplastic mesothelioma.
• Mixed (biphasic) mesotheliomas have both epithelioid and sarcomatoid areas. They make up the remaining 3 out of 10 mesotheliomas.